High frequency receiver



Feb. 10, 1942. H. EICHHOFF HIGH FREQUENCY RECEIVER Filed Jan. 18, 1939Patented Feb. It), 1942 HIGH FREQUENCY RECEIVER.

Herbert Eichhoif, Berlin-Llchterfelde, Germany,

assignor to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof, Germany,-acompany of Germany Application January 18, 1939, Serial No. 251,569

v 3 Claims. It is Well known to adjust the amplificationof .highfrequency receivers by varying the bias potentials-of electrodesthereof. For instance, the grid bias of an amplifying stage is renderedadjustable by means of a potentiometer.

If in the customary manner the control grid voltage is produced with theaid of a resistance Germany January 18, 1938 respect thereto. A,+A'designates the anode battery. If now by varying the priming orbiasing resistance 4 the bias potential of screening grid 1 is alteredin a manner to decrease the anode current, then at the same time thepotentiometer current will increase, whereby the included in the cathodecircuit then it is not practicable to adjust the amplification by vary-I ing the bias of the control grid by means of a potentiometer, becauseit is desirable to connect the oscillatory grid circuit and the negativecontrol grid potentialtoo with the casing.

.If the amplification is adjusted by varying the screening grid bias, adecrease of this potential acts to diminish the anode current. In thiscase, by taking the control grid bias from a potencurrent flowingthrough resistance 3 will remain of constant intensity, the range ofregulation thus not being limited. With constant control grid biastherefore the entire regulating range is available for adjusting thescreening grid potential.

By properly dimensioning the potentiometer resistances it will bepossible to increase the range -of regulation, because any variation ofthe tiometer located in the anode circuit .the bias variation which thecontrol grid undergoes on the anode current decreasing acts inopposition to the bias variation to which the screening gridis-subjected, whereby therange of regulation is f greatly diminished. 1

Also, when decreasing the negative grid bias the grid current range isattained. This isnot desirable since the selectivity of the gridcircuits is impaired thereby. r

In order to avoid thsedisadvantages the in- I vention proposes to adjustthe amplification by means of a method in which the potentiometer.

current controlling the screening grid potential shall flow through theresistance employed for producing the control grid bias so that in thecase of decreasing the screening grid potential 'the potentiometercurrentshall increase without screening grid potential entails anincrease of the drop of potential across resistance 3 and thereby causesthe control grid bias to be varied in the opposite sense.

Similarly, the invention is applicable also to low frequency amplifiers.

What is claimed is:

l. A radio receiver comprising an electron tube having a, control gridand a screen grid and means for adjusting the amplification of said tubecomprising a potentiometer having an adjustable resistance connectedbetween the cathode and screen grid of said tube and a second resistanceconnectedbetween the cathode and the control grid of said tube, and abattery for applying a potential across said resistance in series,whereby the current which passes through the resistance supplying thebiasing voltage to the screen grid is caused to pass also through theresistance for supplying the biasing voltage to the control The biasingpotentials of an indirectly heated by the potentiometer current. Thecontrol grid 5 of this tube is of the potential E of the casing whilethe cathode 6 is of positive potential with grid and upon adjustment ofsaid adjustable resistance a change is caused in the batterycuracterized in this that the resistances of vthe p0- ment to produce achange oi the screen grid voltage will simultaneously cause a higherdrop of potential at the resistance for producing the control grid bias.

HERBERT EIQHHOFF.

